The invention pertains to couplings, joining techniques and cooperating surfaces for transmitting a rotary force. The invention has particular application to cooperating screws and screwdrivers and also to fastening furniture lags to the body of a piece of furniture.
The cooperating screw and screwdriver application of the invention is of greatest importance in those applications where there is no room to hold a screw with one hand while turning the screwdriver with the other hand. The prior art includes magnetic screwdriver blades and/or leaf springs which engage the screw head. Such apparatus has not been wholly satisfactory either because the screw is precariously gripped by the screwdriver and vulnerable to being lost. For example, if there is any axial misalignment between the screw and the cooperating threaded surface, the danger of losing or at least dropping the screw is very significant. The magnetic field produced by the magnetized screwdriver blades is objectionable for many applications such as where a delicate mechanism is being worked on that cannot be magnetized or for devices that include integrated circuits that would be adversely affected. In some other applications stainless steel or non-ferrous threaded fasteners are required and this prevents utilization of magnetized screwdriver blades.
In the quality furniture field it is imperative that the legs and other appendages be secured in a rigid manner. The prior art includes the use of a variety of glues and other fastening means. Presently available means for joining furniture legs have not, in general, been able to provide the degree of rigidity which is possible with the apparatus in accordance with the invention.
It is an object of the invention to provide a coupling apparatus construction that will make a very rigid connection between two cooperating members.
It is another object of the invention to provide a cooperating screw and screwdriver construction which will not be vulnerable to even slight side loads which might cause the screw to be separated from the screwdriver blade.
Still another object of the invention is to provide apparatus which may be used with a wide variety of construction materials including wood, plastics, metal and other materials.
Another general object of the invention is to provide apparatus which is not only sturdy, but which is also relatively invulnerable to inadvertent separations, such as by tipping of the cooperating elements.